JPH06291114A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a single layer of passivation film excellent in moisture resistance and stress is relaxed on the substrate side through simple process by a method wherein the hydrogen contained in a silicon nitride film exists in the form of N-H bond or Si-H bond and the ratio of the quantity of hydrogen in the form of N-H bond and in the form of Si-H bond is varied. CONSTITUTION:An insulation film 2 is formed on a semiconductor substrate 1 and a metallization 3 is formed thereon at selected parts thereof. Furthermore, a silicon nitride film 4 is formed on the metallization 3 and the insulation film 2 not covered with the metallization 3 by ECR-CVD such that the oxygen contained in the silicon nitride film 4 exists in the form of N-H bond or Si-H bond and the ratio of the amount of hydrogen existing in the form of N-H bond and Si-H bond is lower on the surface side of the silicon nitride film 4 than on the substrate 1 side. This constitution relaxes stress of the silicon nitride film 4 on the substrate 1 side and prevents acquisition of hydrogen on the surface side thus realizing a single layer passivation film having good characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a passivation film for protecting the semiconductor device.

[0002]

2. Description of the Related Art Formation of a surface protective film in a semiconductor device,
That is, the passivation technique protects the semiconductor device from various disturbances such as moisture and alkali ions that have an adverse effect on the semiconductor device, and is a very important technique that affects the reliability of the device.

Various types of passivation films have been studied so far. Among them, a silicon nitride film formed by a plasma chemical vapor deposition method (plasma CVD method) has attracted attention because it has relatively good humidity resistance and excellent alkali ion blocking characteristics. However, in general, a silicon nitride film formed by plasma CVD is 5
Since it has a large compressive stress of × 10 ⁹ dyn / cm ² , when such a silicon nitride film is formed on a semiconductor substrate, cracks occur in the silicon nitride film, warp occurs in the semiconductor substrate, and further, It was also a cause of disconnection due to stress migration of metal wiring.
In addition, since the silicon nitride film formed by the plasma CVD method uses SiH ₄ , NH _3, etc. as a film forming material gas, and also uses RF discharge plasma having a low plasma density, Including a large amount of hydrogen is unavoidable, it cannot be said that the moisture resistance is sufficiently excellent,
It has been a cause of deteriorating the characteristics of the semiconductor element and lowering its reliability.

Therefore, for example, Japanese Patent Laid-Open No. 2-168621.
As shown in Japanese Patent Laid-Open Publication No.
A D-PSG film) is used as a lower layer, and a passivation film having a two-layer structure in which a silicon nitride film is formed on the lower layer is often used. In such a two-layered passivation film, PSG having tensile stress as its characteristic
By forming the film and the SiN film having a compressive stress into a laminated structure, the stresses of the both are offset to prevent the occurrence of cracks.

[Problems to be Solved by the Invention]

However, in the passivation film described in the above-mentioned conventional technique, the silicon nitride film is still formed by the plasma CVD method, so that it cannot be said that the moisture resistance is sufficiently excellent as described above. Is. Further, since the passivation film described in the above-mentioned conventional technique has a two-layer structure of a vapor-grown phosphorus glass film and a silicon nitride film, a device for vapor-phase grown phosphorus glass film formation and a silicon nitride film formation Therefore, there is a problem in that the manufacturing process is complicated and the characteristics and reliability of the completed semiconductor device are deteriorated. The present invention has been made to solve the above problems, a single layer with a small number of manufacturing steps, a low hydrogen content, and, by providing a passivation film having a small stress and excellent moisture resistance, It is an object of the present invention to provide a semiconductor device having extremely excellent characteristics and reliability.

[0006]

According to the present invention, in a semiconductor device having a silicon nitride film on a metal wiring layer, hydrogen contained in the silicon nitride film exists in an N--H bond state and a Si--H bond state. The value of (N-H) / (Si-H), which is the ratio of the amount of hydrogen in the N-H bond state to the amount of hydrogen in the Si-H bond state, is on the surface side of the silicon nitride film on the substrate side. It is characterized by being smaller. Further, the invention is characterized in that, in the semiconductor device, the silicon nitride film is formed by an ECR-CVD method.

[0007]

According to the present invention, a passivation film having a small stress and excellent moisture resistance can be obtained in a single layer having a small number of manufacturing steps and with a low hydrogen content, so that the characteristics and reliability can be improved. An excellent semiconductor device can be obtained.

[0008]

1 is a sectional view of a semiconductor device showing the basic structure of the present invention. 1 is a semiconductor substrate, 2 is an insulating film, 3 is a metal wiring layer formed of aluminum or the like, 4
Is a silicon nitride film. This shows that the silicon nitride film 4 as a passivation film is formed on the metal wiring layer 3. The film characteristics of the silicon nitride film greatly change depending on the film forming conditions. The situation is C
Taking a silicon nitride film formed by the VD method as an example,
The details will be described.

FIG. 2 shows an electron cyclotron resonance CV in which SiH ₄ and N ₂ are used as film forming source gases, instead of the conventional plasma CVD method using RF discharge plasma.
It is an infrared absorption spectrum of a silicon nitride film formed by the D method (ECR-CVD method), where the horizontal axis is the wave number and the vertical axis is the transmittance. The unit of the transmittance is shown as an arbitrary unit. The ECR-CVD method is a film forming method achieved by the following principle.

Generally, an electron moving in an electrostatic field receives a Lorentz force and makes a rotational movement. The frequency of this movement,
Frequency of microwave applied, eg 2.45 GHz
When and are matched, resonance absorption occurs, and microwave energy is efficiently absorbed by electron motion. This is the electron cyclotron resonance phenomenon (ECR phenomenon), and its condition can be expressed as follows. w = w ₀ w ₀ = eB / m w: angular frequency of microwave w ₀ : angular frequency of electron cyclotron e: amount of charge of electron B: magnetic flux density of resonance condition m: mass of electron Frequency of microwave from the above conditions Is 2.45 GHz, the magnetic flux density under the resonance condition is 875 Gauss. EC
Resonant electrons of the film forming raw material gas that rotate in R plasma exhibit a diamagnetic effect and are accelerated along the lines of magnetic force while interacting with the divergent magnetic field. Since the plasma is quasi-neutral, the electrons and ions of the film forming source gas have the same acceleration in the magnetic field, and the ions are accelerated out of the magnetic field together with the electrons, forming a plasma flow on the semiconductor substrate to grow the film. Upon incidence, plasma treatment is performed on the substrate surface. In this way, compared with the normal plasma CVD method,
A film can be formed efficiently.

In FIG. 2, the value of the flow rate ratio of SiH ₄ / (SiH ₄ + N ₂ ) is set to 0.15, 0.20, 0.25 and 0.33, and the other conditions are the same. The infrared absorption spectrum of the film is shown. Hydrogen taken into the silicon nitride film is present in the state of N-H bonds or Si-H bonds, the absorption peak around 3350 cm ^-1 and near 2160 cm ^-1, respectively, in FIG. 2 is appeared.
From this result, it can be seen that the size of the peak due to each bonding state changes depending on each flow rate ratio of SiH ₄ . It is known that the amounts of hydrogen in the N—H bond state and hydrogen in the Si—H bond state are respectively calculated by the following formulas based on the peak areas of the N—H bond and the Si—H bond. Here, the amount of hydrogen is the number of hydrogen atoms.
(WA Lanford et al: J. App.
l. Phys. Vol. 49, No. 4, April
(See 1978) (N-H peak area) x 1.4 x 1.36 x 10 ¹⁷
(Pieces / cm ² ) (Si—H peak area) × 1.36 × 10 ¹⁷
(Pieces / cm ² ) The value of the amount of hydrogen obtained from the N—H peak area and the Si—H peak area according to the above formula is divided by the film thickness of the silicon nitride film to obtain the hydrogen content in each bonded state. (Pieces /
The value obtained as cm ³ is shown in FIG. In FIG. 3, SiH ₄ / (Si
H ₄ + N ₂ ) flow rate value on the horizontal axis, and NH in the silicon nitride film when the flow rate ratio of SiH ₄ is changed.
The vertical axis represents the value of the amount of hydrogen in the bonded state and the Si—H bonded state. Moreover, what is shown as Total is
It is the sum of the amount of hydrogen in the N—H bond state and the amount of hydrogen in the Si—H bond state. From this result, the flow rate ratio of SiH ₄ and N-
There is a correlation between the hydrogen content and the hydrogen content of the SiH bond state of H bonding state, increasing the flow rate ratio of SiH ₄ amount of hydrogen in N-H bonding state is reduced, conversely Si- It was found that the amount of hydrogen in the H-bonded state increased. Furthermore, N
It was found that the total amount of hydrogen in the —H bond state and hydrogen amount in the Si—H bond state decreased. In addition, SiH ₄ / (S
iH ₄ + N ₂ ) is the ratio of the amount of hydrogen in the N—H bond state and the amount of hydrogen in the Si—H bond state to the value of the flow rate ratio (N−
H) / (Si-H) is also shown, but SiH
₄ with increasing flow rate ratio (N-H) / (Si-
It was also found that the value of H) tends to decrease sharply and saturate to a value of 1 or less.

FIG. 4 shows the silicon nitride film forming conditions.
The amount of hydrogen in the N—H bond state and hydrogen in the Si—H bond state in the silicon nitride film when only the microwave power as the discharge energy applied to the film forming raw material gas is changed under the same other film forming conditions Amount, the total amount of hydrogen in the N—H bond state and the amount of hydrogen in the Si—H bond state, and (N−H) /
(Si-H) ratio is shown, wherein the horizontal axis represents microwave power, and the vertical axis represents hydrogen content or (N-H) / (Si-.
H) ratio is shown. In this case as well, it is not as remarkable as when the flow rate ratio of SiH ₄ is changed, but again (N−H)
It can be seen that the value of the / (Si-H) ratio changes.

Next, the results of evaluating the stress and moisture resistance of the silicon nitride film will be described, and the relationship between the (N-H) / (Si-H) ratio and the stress and moisture resistance will be described.

First, a method of measuring stress will be described below. Generally, the stress σf of a thin film formed on a semiconductor substrate is given by the following equation. σf = [Es (ts) ² / {6 (1-rs) tf}]
(1 / R-1 / R ₀ ), where Es: Young's modulus of the substrate, rs: Poisson's ratio of the substrate, In the case of a single crystal silicon substrate having a crystal orientation (100), Es / (1-rs) = 1.805 × 10 ¹¹ N / m ² . Therefore, the above equation can be transformed into σf = {(ts) ² / (6tf)} (1 / R-1 / R ₀ ). Here, ts is the thickness of the substrate tf is the thickness of the thin film R is the radius of curvature of the substrate after film formation R ₀ is the radius of curvature of the substrate before film formation. As a method of obtaining the radius of curvature of the substrate at this time, a method of obtaining by a mechanical method, a method of obtaining by an optical method, and the like are conceivable. In the present invention, the substrate surface is irradiated with laser light and the displacement of reflected light The method of obtaining from the quantity is adopted.

Next, the evaluation of moisture resistance will be described. A pressure cooker test is used to evaluate the moisture resistance. In the pressure cooker test, the temperature, humidity, pressure, etc. of the pressure cooker tester are set to be more severe than the conditions under which a semiconductor device is usually used, and the film characteristics after a predetermined time has passed are examined. That is, by performing this test, it is possible to create the same situation as when the semiconductor device is used for a short period of time, usually for several years. Infrared absorption spectrum measuring instrument with Fourier transform function (FT-IR) after pressure cooker test
, The change in the peak of P = O (double bond of phosphorus and oxygen) is investigated. This is the PSG under the silicon nitride film
When the membrane reacts with moisture, the PSG membrane originally has P =
It pays attention to the phenomenon in which the double bond of O is broken and changes to a bonded state of P-O-H. That is, the one having less P = O double bond peak even after being exposed to the condition of high humidity for a long time by the pressure cooker test had less reaction with water, that is, less water penetration. It can be judged that it is good, and it can be considered that it has excellent moisture resistance.

A specific process of evaluating the moisture resistance by the above method will be described. As the sample used for evaluation, a PSG film was formed on a 4-inch silicon wafer by a low pressure CVD method under the following film forming conditions at about 8,000 Å as a substrate. PSG film forming conditions Gas type: SiH ₄ ...... 20 SC
CM 10% PH ₃ /90% SiH ₄ ...... 80 SCCM O ₂ ...... 200 SCCM Pressure: 0.2 Torr Temperature: 430 ° C. Time: 42 min. Moisture resistance was evaluated on the substrate under the above-mentioned conditions by the ECR-CVD method under which various conditions were used to deposit a silicon nitride film of about 1,000 liters. A 4-inch silicon wafer on which a silicon nitride film is formed is divided into four, and one of them is set to an initial value (0
Time) For evaluation, the other three sheets were introduced into the pressure cooker tester for 50 hours, 100 hours, and 200 hours, respectively.
The sample was used after the passage of time. The conditions for the pressure cooker test were a temperature of 121 ° C. and a humidity of 100% R.
H and pressure were 2 atm. FIG. 5 shows a flow rate ratio SiH ₄ / (SiH ₄ + by FT-IR after the pressure cooker test.
It is an infrared absorption spectrum of a silicon nitride film formed with N ₂ ) = 0.15, where the horizontal axis is the wave number and the vertical axis is the absorptance. In addition, the unit of the absorptance is shown as an arbitrary unit. In FIG. 5, it is shown that the peak showing a double bond of P═O appearing around 1330 cm ⁻¹ changes depending on the test time of the pressure cooker test. From the figure, it can be seen that the peak showing the P = O double bond, which appeared when the pressure cooker test was 0 hours, changed so as to disappear as the pressure cooker test time was lengthened. This indicates that, as described above, the P = O double bond is changed to a P-O-H bond, that is, hydrogen is taken into the silicon nitride film. FIG. 6 shows a more detailed analysis of this, that is, a relationship between the pressure cooker test time and the P = O peak area residual rate. In FIG. 6, the peak area of the double bond of P = O was standardized with the initial value (pressure cooker test 0 hours) as 100% to compare the moisture resistance of the silicon nitride film under different film forming conditions. can do.

FIG. 7 shows (N−H) / (Si−) calculated or measured by the method described with reference to FIGS. 3 to 6.
The relationship between the stress and moisture resistance of the silicon nitride film with respect to the (H) ratio is shown. The sample used had a source gas pressure of 1 as film forming conditions.
The pressure cooker test was conducted at a pressure cooker test of 1 × 10 ⁻³ Torr, a microwave power of 700 W, a substrate temperature of 100 ° C. and a flow rate ratio of SiH ₄ and N ₂ as source gases.
It is after 100 hours. In FIG. 7, the stress increases as the absolute value of the value increases, and the minus sign indicates that it is compressive stress. Further, the moisture resistance is an arbitrary unit, and the larger the value, the higher the moisture resistance. As a result, (NH) / (Si
In the range where the value of -H) is relatively large, the moisture resistance is slightly inferior, but a low stress film is formed. On the contrary, in the range where the value of (N-H) / (Si-H) is relatively small, the stress is slightly large. However, it was found that a film having excellent moisture resistance was formed.

The present invention was made on the basis of the knowledge obtained by the various experiments as described above regarding the silicon nitride film. That is, by repeating the experiment as described above, the value of (N-H) / (Si-H), which is the ratio of the amount of hydrogen in the N-H bond state to the amount of hydrogen in the Si-H bond state, is changed. It was found that a silicon nitride film having different stress and moisture resistance can be obtained, and further, the passivation film is required to have low stress and excellent moisture resistance. It was not necessary to know that it was sufficient that the stress was small on the substrate side, and it was sufficient on the surface side that the moisture resistance was excellent, and the inventors invented this. Hereinafter, the present invention will be described in detail based on examples.

First, as shown in FIG. 1, an insulating film is formed on a semiconductor substrate, and a metal wiring layer is further formed on a selected portion of the insulating film. Further, ECR-CVD is performed on the metal wiring layer and the insulating film not covered with the metal wiring layer.
A silicon nitride film is formed by the method under the following conditions. The formation method up to the metal wiring layer and the formation method of the silicon nitride film can be performed in the same manner as the conventional semiconductor device manufacturing process. Deposition pressure: 1 × 10 ⁻³ Torr Microwave power: 700 W Substrate temperature: 100 ° C. Gas type: SiH ₄ , N ₂ gas flow rate: At the start of deposition; SiH ₄ …… 15 SC
CM, N ₂ ... 75 SCCM, at the end of film formation; SiH ₄ ... 33 SCCM, N ₂ ...
... 67SCCM, wherein, at the start gas flow deposition, during film formation ends respectively with as described above, so that SiH ₄ flow rate is continuously increased from the start deposition until the completion of film formation, also, N ₂ The flow rate is controlled by the mass flow controller so as to continuously decrease from the start of film formation to the end of film formation. This state is shown in FIG. When actually forming a film under the above conditions,
The thickness of the obtained silicon nitride film was about 1 μm.

The (N-H) / (Si-H) ratio in the film thickness direction of the silicon nitride film obtained in this embodiment is shown in FIG.
It was shown to. As can be seen from FIG. 9, the silicon nitride film has a large (N-H) / (Si-H) ratio value on the substrate side (base side) and decreases toward the surface side. As a result, as is apparent from FIG. 5, a silicon nitride film having a low moisture resistance on the substrate side but a low stress, and a moderate stress on the surface side but a high moisture resistance can be obtained. Since the SiH ₄ flow rate and the N ₂ flow rate are continuously changed from the start of film formation to the end of film formation, the amount of hydrogen in the N—H bond state and the amount of hydrogen in the Si—H bond state contained in the silicon nitride film. Is continuously distributed in the film thickness direction, the stress is relaxed at the interface with the substrate as a whole of the silicon nitride film, and
On the surface, a sufficient film can be obtained as a passivation film having high moisture resistance.

In the above-mentioned embodiment, the SiH ₄ flow rate and the N ₂ flow rate are controlled so as to continuously increase or decrease from the start of film formation to the end of film formation. It can also be controlled. FIG. 10 shows a mass flow controller for gradually increasing the SiH ₄ flow rate from the start of film formation to the end of film formation, and decreasing the N ₂ flow rate in a stepwise manner from the start of film formation to the end of film formation. The relationship between the silicon nitride film formation time and the SiH ₄ and N ₂ gas flow rates when controlled by The other conditions are the same as those in the above-described embodiment. In this case, as shown in FIG. 11, (N-H) / (Si-H) of the silicon nitride film
The ratio value is large on the substrate side (base side) and gradually decreases toward the surface side. Even in this case, the same effect as that of the above-described embodiment can be obtained.

It is possible to continuously increase the SiH ₄ flow rate and gradually decrease the N ₂ flow rate during the film formation period in the same manner as the above-mentioned two embodiments, and conversely, to change the SiH ₄ flow rate. It is also possible to increase in steps and continuously decrease the N ₂ flow rate. Furthermore, it may be a SiH ₄ flow rate during the deposition period N ₂ flow only continuously or stepwise increased only SiH ₄ flow continuously or stepwise reduced, or N ₂ flow rate is constant as a constant. Furthermore, even if both the SiH ₄ flow rate and the N ₂ flow rate are continuously or stepwise increased during the film formation period, or the SiH ₄ flow rate and the N ₂ flow rate are both continuously or stepwise decreased, the (N-H)
The present invention can be achieved as long as the conditions are set so that the value of the / (Si-H) ratio decreases continuously or stepwise from the substrate side to the surface side. The point is that the value of the (N-H) / (Si-H) ratio after film formation may be reduced continuously or stepwise from the substrate side to the surface side.

As described above, according to the present invention, in the semiconductor device having the silicon nitride film on the metal wiring layer,
Hydrogen contained in the film in the silicon nitride film exists in the N—H bond state and the Si—H bond state, and is the ratio of the hydrogen amount in the N—H bond state to the hydrogen amount in the Si—H bond state ( Since the value of (N−H) / (Si—H) is set smaller on the surface side of the silicon nitride film than on the substrate side, a passivation film having a small stress and excellent moisture resistance can be formed by a single layer with a simple manufacturing process. Obtainable. In the present invention, in the semiconductor device, the silicon nitride film is E
Since the passivation film is formed by the CR-CVD method, the passivation film can be obtained with a low hydrogen content, so that a semiconductor device having excellent characteristics and reliability can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view of a semiconductor device showing a basic configuration of the present invention.

[FIG. 2] EC using SiH ₄ and N ₂ as film forming source gases
It is an infrared absorption spectrum of the silicon nitride film formed by the R-CVD method.

FIG. 3 is a flow rate ratio of SiH ₄ / (SiH ₄ + N ₂ ), the amount of hydrogen in the N—H bond state and the amount of Si− in the silicon nitride film.
It is a graph which shows the relationship between the amount of hydrogen in the H-bonded state, the total amount of hydrogen in the N-H bonded state and the Si-H bonded state, and the value of the (N-H) / (Si-N) ratio.

FIG. 4 shows N- in a silicon nitride film with respect to microwave power as discharge energy given to a film forming source gas.
H-bonded hydrogen amount and Si-H bonded state hydrogen amount, N-
It is a graph which shows the sum total of the amount of hydrogen of a H bond state and a Si-H bond state, and the relationship of the value of a (NH) / (Si-N) ratio.

FIG. 5: F after performing a pressure cooker test
It shows a peak of a double bond of P = O measured by a T-IR measuring instrument.

FIG. 6 is a graph showing the relationship between the pressure cooker test time and the P═O peak area residual rate.

FIG. 7 is a graph showing the relationship between the stress and moisture resistance of the silicon nitride film with respect to the (N−H) / (Si—H) ratio.

FIG. 8 is a graph showing the relationship between the flow rate of SiH _{4 and the} flow rate of N _{2 with} respect to the film formation time of the silicon nitride film in the example.

FIG. 9 is a graph showing the value of the (N−H) / (Si—H) ratio in the film thickness direction of the silicon nitride film obtained by the example.

FIG. 10 is a graph showing the relationship between the SiH ₄ flow rate and the N ₂ flow rate with respect to the film formation time of a silicon nitride film in another example.

FIG. 11 is a graph showing the value of the (N−H) / (Si—H) ratio in the film thickness direction of the silicon nitride film obtained by another example.

[Explanation of symbols]

 1 semiconductor substrate 2 insulating film 3 metal wiring layer 4 silicon nitride film

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Claims (6)

[Claims] 1. A semiconductor device having a silicon nitride film on a metal wiring layer, wherein hydrogen contained in the silicon nitride film exists in an N—H bond state and a Si—H bond state, and the N—H bond state. The ratio of (NH) / (Si-H), which is the ratio of the amount of hydrogen in the above to the amount of hydrogen in the Si-H bond state, is smaller on the surface side of the silicon nitride film than on the substrate side. apparatus. 2. The value of the (N-H) / (Si-H) ratio decreases continuously or stepwise from the substrate side to the surface side. Semiconductor device. 3. The semiconductor device according to claim 1, wherein the silicon nitride film is formed by an ECR-CVD method. 4. The semiconductor device according to claim 1, wherein the silicon nitride film is a passivation film. 5. The silicon nitride film according to claim 1, wherein the total amount of hydrogen contained in the film is 3 × 10 ²² / cm ⁹ or less. The semiconductor device according to item 4. 6. The hydrogen content ratio (N—H) / (Si—H) in the silicon nitride film depending on the bonding state is 4 or more on the substrate side and 2 or less on the surface side. The semiconductor device according to claim 1, claim 2, claim 3, or claim 4.